1. Field of the Invention
The present invention relates to a heater unit and a battery structure with heater including the heater unit.
2. Description of Related Art
Batteries such as nickel-metal hydride storage batteries have been watched as power sources of portable devices and power sources of electric vehicles, hybrid electric vehicles, and others.
However, the batteries such as nickel-metal hydride storage batteries have problems that discharge capacity is apt to decrease during cold conditions, failing to provide adequate output power. If such battery is used as a power source of an electric vehicle, a hybrid electric vehicle, or the like, for instance, it could not generate sufficient output power in low-temperature conditions, e.g., in a cold region where temperatures may fall to sub-zero.
In recent years, some techniques for solving the above problems by attaching a heater to a battery to heat the battery by use of a household power source have been proposed (e.g., Jpn. unexamined utility model publication No. 60(1985)-192367).
Jpn. unexamined utility model publication No. 60(1985)-192367 discloses a battery structure with heater, in which a sheet heater is placed on a bottom of a housing case made of a heat insulation material and two batteries are arranged in contact with the sheet heater in a container.
However, the technique disclosed in the above publication '367 may not heat the battery sufficiently. This disadvantage results from the following reasons. In some cases, deformation such as warp or distortion occurs in a bottom of a container made of a heat insulating material. If the sheet heater is also deformed, warped or distorted due to the deformation of the container, a gap is likely to be formed between the sheet heater and the battery. In this case, furthermore, the heat of the sheet heater is hard to conduct to the battery. This may cause an excessive increase in temperature of the sheet heater (part or whole of the heater) itself.